gas gage needle wiggle

[John L.]

I am preparing for PV of my 64 Coupe. My gas gage has a wiggle it that is intermittant, but does seem to only do it when the car is moving, or someone is getting in/out or bouncing the fender...it never wiggles at idle standing still. And it doesn't move when any other electrical device is turned on or off...While driving, it can remain steady...then all of a sudden it starts jumping around ...and its not a slow movement, its eratic and jerky. The mechanics are trting to tell me that is how it is with an old gas tank with no baffles...as the gas sloshes around so does the gage. Is that true and will that make it throuhg PV? Any advice?

[Joe R.]

Re: gas gage needle wiggle

The small gauges have a viscious fluid in them to dampen the oscillation of the pointer (needle). After forty to fifty years the fluid leaks out or dries up and the pointer oscillates readily. This action is seen more in the amp gauge as it's subject to spikes of current in the electrical circuit.

You will need to replace your gauge if you want it to operate properly during PV.

JR

[John L.]

Re: gas gage needle wiggle

Thanks Joe...I had gage rebuilt...I guess what I am asking is is the wiggle normal or not...should it move some as the mechanics are trying to tell me or should it pretty much stay motionless most of the time? Thanks,

[Edward J.]

Re: gas gage needle wiggle

John, does the gage move around no matter where the fuel level is in the tank?

[Michael O.]

Re: gas gage needle wiggle

John, I too, have a 64 and the needle on the gas gauge moves when I come to a stop or experience some other activity that results in the gas sloshing around in the tank. In my opinion, your mechanic is right. Without the baffles, it just reading where it thinks the gas is at that moment.

[Dick W.]

Re: gas gage needle wiggle

John, check your PM's. I sent you an "Old Indian" trick that works to get you past PV

[Ronald L.]

Re: gas gage needle wiggle

Dick, Is that max out the fuel tank?

[Pat M.]

Re: gas gage needle wiggle

Not sure if it's the same for C2s, but for eary C3s the PV manual recommends that the tank not be maxed out, and states that the absence of minor fuel needle fluctuations during braking, cornering, etc., is a cause for failure. What does the 64 PV manual say?

[Dick W.]

Re: gas gage needle wiggle

Dick, Is that max out the fuel tank?

Nope, guage reading is base on resistance to ground. Learned this trick when we restored a '63 Z06 tanker that had a bad sending unit. Ever try to find one of those units??

[Ronald L.]

Re: gas gage needle wiggle

That's probably one of the rarest C2 parts.

[Jack H.]

Re: gas gage needle wiggle

"guage reading is base on resistance to ground."

Yes and no here... The mid-year cars employed a unique circuit topology based on a Whetstone bridge layout. The circuit is TOTALLY INDEPENDENT of the level of battery voltage and the pointer needle simply reflects the degree to which the four legs of the bridge are in balance.

It was unique enough that the 1963 Corvette Shop Manual devoted a theory of operation discussion on the circuit (Section 12, pages 13-14). And, the circuitry difference(s) warranted a dedicated troubleshooting chart (Section 12, page 26).

One thing that's unique to this system is it has TWO separate ground points that BOTH have to be intact for proper gauge operation. One ground is at the tank sender (the pot windings in the sender form half of the Whetstone bridge).

The second ground is at the gauge in the dash instrument cluster. That's formed by how well the gauge is physically screwed into the instrument cluster AND the cluster's grounding integrity via the dash cluster.

I've seen some cases where guys got in a rush to R&R a dash gauge and failed to torque the mounting screws properly resulting in intermittent electrical continuity, especially when shock/vibration are afoot...

[Rick A.]

Re: gas gage needle wiggle

Jack said: "I've seen some cases where guys got in a rush to R&R a dash gauge and failed to torque the mounting screws properly resulting in intermittent electrical continuity, especially when shock/vibration are afoot..."

This is exactly what caused me to have problems when I was trying to pass PV with my 1963 Z06! Torqued the screws and no more problemos!

[Terry M.]

Re: gas gage needle wiggle

The small gauges have a viscious fluid in them to dampen the oscillation of the pointer (needle). After forty to fifty years the fluid leaks out or dries up and the pointer oscillates readily. This action is seen more in the amp gauge as it's subject to spikes of current in the electrical circuit.

You will need to replace your gauge if you want it to operate properly during PV.

JR

Joe,

I am sure you have seen more Corvette gauges than I have, but my industrial experience is only more expensive and precise gauges are fluid damped. Automotive gauges are anything but expensive and/or precise. I have yet to see an OEM automotive gauge that is fluid damped -- but I am eager to learn.